Try returning to the Normandy and see if Traynor mentions new messages at your terminal.
No, I was able to invite her after the initial round that she had set up.Do you have any one else left to invite to your apartment or go see on the strip? Traynor mentioned the new messages for me only after I cleared the current set of Invites on my apartment terminal.
Whereabouts are you in the Main Storyline? It may be that you aren't far enough in the storyline to unlock the last part with her. Is she still in Purgatory on the Citadel?
Maybe get to just before the attack on the Illusive Man's base then (That is if you aren't there already)? That's when I started the DLC and was able to get everything.
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